<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>嵌套div示例</title>
    <style>
        .outer {
            width: 300px;
            height: 300px;
            background-color: lightblue;
            padding: 20px;
        }
        .inner {
            width: 100px;
            height: 100px;
            background-color: lightcoral;
        }
    </style>
</head>
<body>
    <div class="outer">
        外层div
        <div class="inner">
            内层div
        </div>
    </div>
</body>
</html>